Without limiting the scope of the invention, its background is described in connection with semiconductor devices, as an example.
Heretofore, in this field, the epitaxial growth of insulators on semiconductors has been an important step in the fabrication of various electronic devices, such as metal-insulator-semiconductor field effect transistors (MISFETs), silicon on insulator (SOI) technology, three dimensional integrated circuits, etc., as well as novel devices that cannot be achieved with amorphous insulators. Epitaxial growth of Group II fluoride on silicon has been studied extensively because of its technological and scientific interest. As one of the most promising candidates in this area, the CaF.sub.2 /Si couple has attracted considerable attention. From a materials preparation point of view, CaF.sub.2 is a relevant choice among the fluorides for deposition on silicon because it fits several important criteria for a good epitaxial system, i.e. small lattice mismatch and similar cubic structure. Previous studies have shown that the chemical and structural properties of the CaF.sub.2 /Si interface vary under different deposition conditions and that these variations can significantly change the electrical characteristics of a system incorporating this interface. Co-assigned patent application Ser. No. 07/704,535 describes a method that allows the growth of films in which the orientation of the CaF.sub.2 film is essentially identical to that of the silicon substrate, a characteristic which is important for good interface properties.
Additionally, the epitaxial growth of Al on Si has attracted increasing interest because it might offer a solution to the reliability problems caused by polycrystalline Al, which is widely used in the metallization of integrated circuits. Recent studies have shown that the electromigration resistance of single crystal Al is significantly better than that of polycrystalline Al. Improvement in thermal stability has also been reported when single crystal Al is used. Similar advantages exist for epitaxial conductors on insulators. Yamada and Takagi, IEEE Transactions on Electron Devices, vol. 34, 5, May 1987, report the growth of single crystal Al on epitaxial CaF.sub.2 using ion cluster beam (ICB) epitaxy. ICB relies on high electric fields to provide ions with kinetic energy, and by so doing allows the growth of epitaxial films using low substrate temperatures.